JMO, but the only way to remove old rust, and maybe most of the pitting, from a receiver's bolt lug seats is by lapping with a fine automotive valve grinding compound - which is probably going to exasperate what might already be a rifle with excessive headspace.
I would plug the chamber throat, and fill the chamber and bolt lug area of the receiver wuth household Hydrogen Peroxide - then let it sit/soak for a few days to dissolve the blood.
I'd then lap the surface rust only with one extremely light-pressure pass of the bolt lungs coated with the lapping compound, then clean & lube both bolt & receiver- and try the action to see how you've progressed. Baby steps.
(The lapping is done with a stripped bolt given backward pressure while opening/closing - to simulate cartridge backpressure)
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